1. Field of the Invention
This invention relates to an oscillating loop taker which preferably employed in a sewing machine for household and industrial uses.
2. Description of the Prior Art
FIG. 1 is a front elevational view showing a conventional oscillating loop taker 1, FIG. 2 is a perspective disassembled view of the oscillating loop taker 1 shown in FIG. 1, and FIG. 3 is a sectional view of the oscillating loop taker. The oscillating loop taker 1 to be employed in a sewing machine for household and industrial uses includes a bobbin case holder 3 supported by a bobbin case holder rib 2 being inserted in a hook groove formed on an inner peripheral surface of a cup-shaped hook body, not illustrated herein, a driver member 4 by which the bobbin case holder 3 is driven by half revolutions in the directions of arrows A1 and A2, and a bobbin case 7 in which a bobbin 6 in which a bobbin thread 5 is wound is accommodated. A rotation restraining member 7a is integrally formed with the bobbin case 7 and fits in a fitting recess of a bobbin case holder clamper, not illustrated herein, thereby preventing rotation of the bobbin case 7 upon rotation of the bobbin case holder. A lower spindle of a sewing machine is coaxially fixed at a mounting portion 8 of the driver member 4 and is driven by half revolutions rotary axis line l. When the driver member 4 rotates in the direction of an arrow A1, one end portion 9 in the peripheral direction thereof is brought into contact with a respective contacting portion of the bobbin case holder 3, thereby causing the bobbin case holder 3 to rotate in the direction of arrow A1, with the bobbin case 7 however being prevented from rotating. As end portion 9 of a driver member 4 reaches an upper dead point, the direction of rotation thereof is reversed to cause the driver member 4 to be driver for rotation from the direction of arrow Al to the direction of arrow A2. At this time, an opposite end portion 11 in the peripheral direction of the driver member 4 is brought into contact with an inner surface of a recess formed in the vicinity of a wedge 12 of the bobbin case holder 3, thereby causing the bobbin case holder 3 to rotate in the direction of arrow A2, with the bobbin case 7 however being prevented from rotating.
In the oscillating loop taker 1 which can be driver for half turns or half revolutions as described above, a needle thread carried by a needle 14 which can vertically reciprocate is caught by the wedge 12 and the bobbin case holder 3 is rotated by a half turn in the direction of arrow A1 by the driver member 4, thereby causing a needle thread loop to be formed. At this time, the needle thread is arranged at a lower portion of the loop taker as shown by the dashed line 15 and moves in the direction of an arrow 18, sliding along with a guiding face 17 of a thread guiding projection 16 which forms the recess 13 together with the wedge 12. Then the needle thread 15 transfers to the outer peripheral surface of the bobbin case 7 by vertical movements of a balance (not illustrated) of the sewing machine body. Thus, as the balance is elevated, the needle thread 15 shifts over, sliding on the outer peripheral surface of the bobbin case 7. The needle thread 15 which is thus pulled upwards by the balance is engaged with the bobbin thread which is drawn out from the bobbin 6 in the bobbin case 7, thereby causing a swing joint to be formed.
When the needle thread 15 transfers to the outer peripheral surface of the bobbin case 7 from the wedge 12, the bobbin case holder 3 reversely turns in the direction of arrow A2 and returns to the initial position (the solid line position shown in FIG. 1). And the bobbin case holder 3 is again driven in the direction of arrow Al and catches the needle thread carried to the vicinity of the wedge 12 by a downstroke movement of the needle 14, thereby causing a need thread loop to be formed. A series of movements as mentioned above is repeated, thereby causing consecutive sewing joints to be formed.
When the oscillating loop taker 1 is utilized in a sewing machine for household or industrial use, then when the bobbin thread 5 of the bobbin case 6 is consumed, the bobbin 6 from which the bobbin thread 5 has been consumed must be replaced with a bobbin in which new bobbin thread has been wound. Especially, in a sewing machine for industrial use, the sewing speed of which is fast and the dewing volume of which is large, the bobbin 6 must be replaced frequently, and the sewing efficiency thus will be reduced.
The winding capacity of the bobbin thread 5 can be increased by enlarging the diameter D of the bobbin 6 and the width B in the axial direction of the bobbin 6. However, if the diameter D of the bobbin 6 is enlarged, the bobbin case holder 3 must be accordingly enlarged. If the bobbin case holder 3 is enlarged, the needle thread loop is also enlarged, thereby causing not only thread tightness to be worsened and the likely production of balls of thread, but also vibrations accompanying the half turn movements of the bobbin case holder will be increased and noise accordingly will be increased. Also, if the width B of the bobbin 6 is enlarged, it will become difficult for the needle thread loop to transfer onto the bobbin case 7. As a result, undesirable tension operates on the needle thread to cause the thread tightness to be worsened, and balls of thread may be produced with a reduction in sewing quality.